The broad aim of this proposal is to investigate the role of phosphoinositides in membrane function. Circumstantial evidence suggests that the enhanced turnover of phosphatidylinositol (PI), an effect which is produced in secretory tissues by a variety of compounds, including hormones and neurotransmitters, precedes and is necessary to the involvement of calcium ions in stimulus-secretion coupling. We plan to test this hypothesis directly as follows: 1) We will synthesize compounds which bear structural similarities to PI by additoon of hydrophobic moieties to water-soluble degradation products of native PI. 2) Since the primary effect on PI metabolism is apparently to stimulate hydrolysis of the lipid by PI phosphodiesterase, we will determine the potency and specificity of these substances to inhibit soluble brain PI phosphodiesterase, as compared to other enzymes of phosphoinositide metabolism. 3) Using the isolated pancreatic islet, we will determine the ability of the inhibitors to block glucose-stimulated insulin secretion and, if experimentally possible, to prevent the inhibition of PI breakdown. If blockade is obtained, we will investigate the effect of inhibitors on movements of ions which accompany insulin secretion. Complementary to these studies, we will purify soluble brain PI phosphodiesterase by affinity chromatography and characterize the purified preparation.